1. Field of the Invention
This invention relates to a method and apparatus for joining branching fittings to conduit lines and particularly, for heat welding thermoplastic branching fittings to thermoplastic pipe mains.
2. Prior Art
During the last decade, the growth in industrial applications of thermoplastic piping for gas, water, sewage and chemical product handling has been phenomenal. The tremendous increase in use of thermoplastic piping and fittings has resulted from the realization of their unique properties of strength, durability, flexibility, resistance to attack by chemicals and other elements, and economy. These properties make thermoplastic systems safe, serviceable, rugged and economical.
With the tremendous growth in the use of thermoplastic pipes and hardware has come the need for methods and tools for joining the pipe to form desired channels of distribution. Such distribution channels are more readily constructed with thermoplastic components since the piping and hardware may be joined or repaired through the use of a heat fusion method of welding. In this welding method, the surfaces of the members to be welded are first heated to the point where they begin to melt and then are pressed together until they solidify. The pipes and fittings to be joined vary in size. Fittings may be joined to pipe measuring twelve inches in diameter or larger. Particularly where such large pipe and mating fittings are used, equipment and techniques are required to assure that the fitting is properly aligned with the pipe, that the proper pressure is exerted on the fitting against the pipe and that the apparatus is quick and easy in its operation.
Joining apparatus presently used generally lack accurate means of exerting pressure on the fitting against the pipe main, means for quickly withdrawing the fitting from the heater element when the surfaces are properly plasticized and means for quickly engaging the fitting against the pipe before any cooling of the surfaces to be joined occurs. The absence of any one of these means may form a joint unacceptable or faulty for the purposes intended. Proper alignment is necessary because a precise and uniform contact pressure must be achieved during welding. Accurate control of the pressure on the fitting against the pipe is critical since too little contact pressure will result in an ineffective weld whereas too great a pressure will cause excessive displacement of the plasticized material leaving excessively cool material at the point of contact between the fitting and main thereby creating an insufficient weld. The quick operation of the unit is necessary in that the weld will be of sufficient strength only if the contact material is properly plasticized at the time of joining. This can best be accomplished by heating the surfaces to be joined to the precise temperature required followed by immediate contact between the mating surfaces.